It is known in the art that commutation of a brushless DC motor requires sensing the position of the rotor of the motor or of the shaft of the motor. A switching circuit will apply DC voltage to one or another of the coils within the motor depending upon the position of the rotor. In order to start the motor effectively, the sensor should be able to measure the position of the rotor when it is stationary.
Presently used techniques employ either magnetic sensors, both Hall-Effect and magnetoresistive sensors, or optical sensors. Optical sensors are notoriously susceptible to dirt and sensors with sufficient resolution are relatively expensive. Hall-effect sensors have a history of reliability problems when operated in severe environments.
Rotor position techniques currently in use require active semiconductor devices for their operation, further reducing the reliability of the device.